I'm with Jason on the sub -- the S-1 speakers will really sound incredible with something else picking up the bass, but without a sub, the S-1s are fairly helpless under 100 Hz. My Icon and S-1 are sitting in their shipping box until my sub arrives. I had them out to listen to them extensively as I was writing the review for Techgage, and I was thrilled with their clarity, but the lack of bass has kept me listening to my Cambridge Soundworks MicroWorks II a little longer. (BTW, I'm convinced you can't do better than the MWII for under $150.)
You may or may not decide to use the NuForce sub - any* sub will work with the S-1 as long as you provide the right cables and integrate it well into the room and the system. Personally, I'm looking for something that can move a bit more air, so I'm going to try the 180-watt Velodyne Impact-Mini (since I love the MiniVee that I've got in the living room). The Impact-Mini arrives this week, and a full report will follow.
*The quantity and quality of bass from the sub will depend on the subwoofer's quality. "Work" in this case means you can send signal to it and cause it to make sound.